(1) Field of the Invention
The present invention relates to an incubator apparatus and a method for preparing an aerobically cultured food from a plant material. In particular, the present invention relates to an incubator apparatus and a method for aerobically culturing a plant material, primarily soybeans, provided with a beneficial microorganism, preferably a fungus of the genus Rhizopus, to prepare a Tempeh. The soybean can also be extended with a portion of barley cereal grain or other cereal grains.
The incubator apparatus is comprised of a container for a water bath. A water circulation means having a sensor controlled heater coil as a first heater means warms the water bath during the first half of the incubating process and causes the water bath to flow throughout the container. This helps to maintain uniformity of temperature in the water bath while the plant material is being aerobically cultured to form the Tempeh. The sensor also controls the cooling of the water bath during the second half of the incubation process. A second heater means is mounted in the container for heating the water bath to a high temperature.
To prepare the Tempeh, shallow metal trays, preferably made of stainless steel, are filled with the plant material and supported on racks so that the trays are partially immersed in the water bath. The trays are preferably arranged side-by-side on the racks as units and a plurality of racks are mounted in parallel in the water bath. The trays can be of various sizes, although it is preferred that they have a depth of about 1 inch (2.54 cm) and the plant material is provided in the trays up to a depth of about 0.75 inches (1.9 cm). A removeable lid or cover mounts over and around the trays filled with the plant material. The cover can be a single, continuous member covering all of the tray units in the water bath, or there can be individual covers, preferably for each side-by-side tray unit. A lower rim portion of the cover is immersed in the water bath to seal the cover over and around the trays. An aerating means is centrally located in the water bath between each side-by-side tray unit so that an airflow bubbles up through the water bath and moves over the plant material held in the trays. The airflow exits through perforations provided in the cover, away from the aerating means. During the culturing process, the microorganisms aerobically grow to produce enzymes that act on the proteins, carbohydrates and the oil in the plant material. Tempeh produced in the incubator apparatus is a palatable and nutritious food that can be eaten as is or further prepared by cooking.
After the microorganisms have cultured the plant material, the second heater means is used to elevate the temperature of the water bath beyond that which is suitable for growth of the microorganisms. This kills the microorganisms and pasteurizes the plant material. The trays are then uncovered to cool the cultured food, and the cultured food is cut into useable portions and packaged for later consumption.
(2) Prior Art
For centuries in Asiatic cultures and particularly in Indonesia, Tempeh has been a valuable and important food produce prepared by fermenting and culturing whole dehulled soybeans or soybean grits or meal with pure cultures of beneficial fungi or microorganisms. Tempeh is an important food in Asiatic cultures because soybeans grow readily in moderate climates and because soybeans contain proteins, carbohydrates, fats, vitamins and other nutrients, but have no cholesterol.
Historically, Tempeh is prepared in small scale operations by first soaking whole soybeans in water. The soaked, wet soybeans are then dehulled and boiled in water to soften the beans and destroy any contaminating microorganisms. The cooked soybeans are then spread out in thin layers to allow the water to drain and evaporate from the surface of the soybeans. The air dried soybeans are then mixed with a starter comprising portions of old Tempeh containing a mixture of molds, bacterial and other microorganisms. The moist inoculated soybeans are then wrapped tightly in banana leaves and the material is allowed to culture at room temperature until the soybeans are completely molded. This product is known as Tempeh, which can be eaten as is or sliced into thin slices, dipped into a salt solution and fried in a vegetable oil.
The culturing of soybeans destroys the bad odor and bad flavor of soybeans by apparently causing the microorganisms to produce enzymes that act on the proteins, carbohydrates and the oil in the soybeans to make the Tempeh palatable and nutritious and to give a desirable flavor. The microorganisms mainly responsible for Tempeh culturing are stated to be Rhizopus oryzae and Aspergillus oryzae. These microorganisms require aeration for growth and the formation of enzymes.
The prior art culturing of soybeans to make Tempeh has numerous objectionable steps. Since the microorganisms responsible for Tempeh are aerobic, during the culturing process the soybeans must be spread out in layers that are relatively shallow in depth. This means that the area of the soybean layers must be large. Thus, the use of large area trays has proliferated in recent times for commercial production of Tempeh. Martinelli and Hesseltine (1964) Food Technology, Vol. 18, No. 5 found that large metal trays were excellent for commercial Tempeh production because they were more sanitary and allowed for easier removal of the Tempeh from the container in comparison to wooden trays (unless the wooden trays were lined with perforated plastic sheeting). The metal trays were reported to preferably be large aluminum trays instead of large stainless steel trays. However, the use of aluminum in prolonged contact with food is being questioned in relation to its possible implication in causing Alzheimer disease. Since stainless steel is a poor heat conductor, having less than 10 percent of the thermal conductivity of aluminum, there tends to be a build-up of heat at the center of the tray that causes spoilage there. Plastic school lunch trays can also be used as Tempeh containers if the tray material is approved for contact with fermenting foods.
In the prior art methods, the layers of soybeans must also be covered by some film. The use of banana leaves is extremely primitive, can cause contamination and is limited to those areas tropic enough to support growth of banana trees. More recently, Martinelli and Hesseltine (1964), discussed previously, have suggested the use of a thin sheet of polyethylene film, which is perforated every 2 to 3 inches with a nail. The soybeans can also be covered with a reusable sheet of stronger polyethylene, rigid Plexiglas.RTM. or an imperforated sheet of wax paper.
Using an inoculum consisting of a portion of old Tempeh is very unsanitary. The old Tempeh can be contaminated by a variety of molds, bacteria and yeasts, and this method of preparation is practiced at the expense of the nutritional benefit of the Tempeh. Also, since the inoculum is highly variable as to the viability of the mold even when the inoculum is relatively pure, culturing time requirements for the Tempeh are extremely variable, as is the product itself.
The most commonly practiced prior art method of making Tempeh consists of incubating a layer of soybeans covered with a flexible plastic sheet modified with aeration perforations. The incubation process takes place in an incubation room having an agitated airflow that is uniformly heated or cooled and with a consistent humidity. The problem is that agitation of the airflow often leads to blackened areas on the Tempeh where the airflow meets the microorganisms at the perforated holes. This contact with the fast moving airflow causes the microorganisms to sporulate prematurely and produces undesirable black spores. The greater the agitation of the airflow to ensure that the air in the incubation room does not stratify, the greater the occurrences of premature sporulation. Furthermore, it is difficult to accurately control the humidity in the incubation rooms. If the airflow is slightly drier than optimum, the black spore problem is increased. There is thus a need for Tempeh and other fermented foods having a more uniform appearance and useful shape (most of the Tempeh produced today is incubated in 8 ounce perforated plastic bags). There is also a need for the Tempeh to be pasteurized and ready to be consumed.
U.S. Pat. No. 3,228,773 to Hesseltine et al describes an improved method of preparing Tempeh by fermenting soybeans with certain phycomycetous fungi of the order Mucorales, genus Rhizopus. The soybeans are soaked overnight, the seed coats are removed and the whole soybeans may be cracked into large grits. The soybeans are then softened and moistened by soaking in water and then boiled to sterilize and further soften the soybeans. Excess water is drained and the soybeans are cooled below 104.degree. F. (40.degree. C.) and then inoculated with a spore suspension of Rhizopus spores. Species of this genus which are operative to give acceptable results include Rhizopus oligosporus, R. arrhius, R. acglamydosporus, R. formosaensis, R. stolonifer and R. oryzae. The soybeans are then cultured at a temperature of between 77.degree. and 99.degree. (25.degree. to 37.degree. C.). The soybeans are cultured in conventional non-toxic, plastic bags modified by the presence of 0.02 inch diameter perforations located not over 0.5 inches apart. The soybeans are also described as being cultured in perforated flexible, plastic tubing having a diameter of 3.5 inches (9 cm). In either example, the resulting Tempeh must be removed from the plastic container and then cooked to prepare the Tempeh as a consumable food. There is a need for Tempeh and other fermented foods which are pasteurized and ready to be consumed as a food.
U.S. Pat. No. 3,243,301 to Hesseltine et al describes a process of making a novel variety of Tempeh, not exclusively from soybeans. The novel Tempeh is made by subjecting cereal grains such as wheat, rye, rice, barley and oats or mixtures of the same, alone or in combination with pre-treated soybean grits, to the action of the mold Rhizopus oligosporus. This mold is characterized by the presence of large amounts of both proteolytic and lipolytic enzymes, but little or no amylolytic enzyme. Any appreciable amount of the latter class of enzyme would break down the cereal grain starch to simpler sugars that would then be fermented to disagreeably tasting organic acids and highly colored materials. Thus, the closely related fungis Rhizopus oryzae and the mold Aspergillus oryzae on substrates comprising a cereal grain produce darkly colored, ill-smelling, and unacceptable products.
U.S. Pat. No. 3,981,234 to Nelson et al describes an apparatus for the preparation of a soybean beverage base. This apparatus produces a relatively coarse ground slurry consisting of water and approximately 12 percent by weight of soybean tissue.
U.S. Pat. No. 4,248,141 to Miller. Jr. describes a method and apparatus for debittering soybeans caused by enzymes lying next to the bean surface directly beneath the skin. The end product is dry, dehulled soybean halves, suitable for the usual raw soybean use.
Shurtleff & Aoyagi describe the process of making Tempeh in Tempeh Production, The Book of Tempeh: Volume II, published by New-Age Foods, 1980. Tempeh is also discussed in Soyfoods, Vegetarian Times, pages 35 to 39, November 1987.
Other prior art less directly related to the present invention includes U.S. Pat. Nos. 1,513,174 to Kruger, 4,013,869 to Orts and 4,848,2161 to Robau. Kruger describes a grain soaker wherein grain held in the soaker can be immersed in water for a period of time and afterwards raised and permitted to drain. Orts describes a tortilla warmer and hydrator. The device is particularly useful for warming and hydrating tortillas that have been cooked at an earlier time and have subsequently become cold and hard. Robau describes a steam-heated milk warmer.
What is needed is a method and an incubator apparatus for the commercial production of a pasteurized Tempeh from a plant material, which is preferably soybeans. The cultured product needs to be produced in a consistent manner, in a useful shape and be reproducible on a large scale.